Thanks everyone for the suggestions.
However - NOTHING worked.
Got BBSAK - nice tool.
Tried every permutation of Load OS / pull battery / Wipe Device available.
Still hangs in the same place - this with the OS Image I got from the official BlackBerry / AT&T page.

Tried all that 'start from scratch' stuff with the 'downrev' OS image (what I was running happily with before). SAME thing.

Off for some quality time with the AT&T store this afternoon - we'll see what they have to say...